Region 1: EPA New England

Carbon Monoxide

Carbon Monoxide Maintenance Areas In New England

Map of Carbon Monoxide Maintenance Areas In New England

Carbon monoxide (CO) is a colorless, odorless gas that can increase the severity of lung ailments, cause dizziness, fatigue, nausea, and even death. EPA has defined the national ambient air quality standard (NAAQS) for carbon monoxide as nine parts per million averaged over an eight-hour period, and this threshold cannot be exceeded more than once a year or an area would be violating the standard.

In New England, fuel combustion in residential housing, businesses, industry and utilities accounts for 10 to 20 percent of the total CO emissions, while mobile sources (cars, trucks, buses and off-road equipment such as marine engines and construction equipment) account for 80 to 90 percent. In the past, carbon monoxide air quality problems were usually localized in nature, and mostly found at congested intersections with significant motor vehicle traffic.

EPA and the States have implemented many programs during the last three decades that have reduced CO emissions. At the national level, these measures include establishing national standards for tailpipe emissions, new vehicle technologies, and clean fuels programs. State emissions reduction measures include inspection and maintenance (I/M) programs and transportation management programs.

A gradual decease in CO emissions has occurred nationwide over the last two decades. Historically, areas in Connecticut experienced the highest CO levels of anywhere in New England, primarily in the cities of Hartford, New Haven, Bridgeport, Stamford, and points to the south and west. In the early 1980s these areas experienced many days above the NAAQS, but concentrations have dropped significantly and have fallen below the NAAQS, and the entire State of Connecticut is now designated as attainment for Carbon Monoxide. This has also been the case in Providence, RI, the Boston metro area, the New Hampshire cities of Nashua and Manchester, and the Massachusetts cities of Worcester, Springfield, Waltham, and Lowell.

Since a monitor must exceed the NAAQS of 9.0 parts per million more than once in a year to be in violation of the standard, EPA views the second highest eight-hour value recorded each year as the most critical indicator of attainment. Therefore, the graphics below depict the trend in the second highest eight-hour average recorded at CO monitors in New England and shows that the second high has dropped significantly over the last 20 years. Between 1988 and 1997, the number of exceedances of the CO NAAQS in the United States dropped by an astonishing 95 percent. Today, all CO monitors in New England are well below the standard, with some states considering shutting down monitors that routinely measure such extremely low concentrations.

Click for larger graph of Connecticut Carbon Monoxide Monitoring

Click for larger graph of Rhode Island Carbon Monoxide Monitoring

Click for larger graph of Massachusetts Carbon Monoxide Monitoring

Click for larger graph of New Hampshire Carbon Monoxide Monitoring

To keep CO levels low, EPA will continue to work with engine and fuel manufacturers to ensure that emissions remain relatively low. EPA will also work with the states to ensure that the air in New England is monitored to be sure that we maintain low levels of carbon monoxide.

For a copy of the report entitled "Carbon Monoxide in New England, A success Story," contact Ariel Garcia ( or (617) 918-1660).